Waveguide coupling device



March 1959 R. s. ELLICYJTT 2,878,453

WAVEGUIDE COUPLING DEVICE Filed Aug. 1, 1956 lnventor.

v Attorney.

United States Patent WAVEGUIDE COUPLING DEVICE Robert S. Elliott, Los Angeles, Calif assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application August 1, 1956, Serial No. 601,523

Claims. (Cl. 333-33) This invention relates to a coupling device torwaveguides and more particularly to a rectangular-to-coaxial waveguide transition.

In microwave transmission lines, it is often desirable to effect a transition from a hollow waveguide to a co axial waveguide. This raises the problem of providing a transition between the dominant TE -mode in a rectangular waveguide and the principal TEM-mode in a coaxial Waveguide. Heretofore, this transition problem has been solved by coupling the two waveguides to one another through an excitation element. This excitation element was adapted to be excited by the existing mode in one waveguide and when so excited to radiate or set up the desired mode in the other waveguide. A comprehensive summary of such waveguide coupling devices is published in Microwave Transmission Circuit's" by George A. Ragan, published in the MIT Radiation Laboratory Series, volume 9, page 314 et seq.

Interposition of such excitation elements inherently limits the amount of power which may be transferred from one waveguide to another. Furthermore, a waveguide coupling including an excitation element provides a mode transition which is often highly sensitive to changes of frequency and which is therefore useless for broadband operation.

It is therefore an object of this invention to provide a waveguide coupling device which is adapted to mode couple a rectangular waveguide directly to a coaxial waveguide without the interposition of an excitation element.

It is a further object of this invention to provide a new and novel rectangular-to-coaxial waveguide transition I which is adapted to handle microwave energy of very high power and which is very broad-band in operation.

It is a still further object of this invention to provide a unity waveguide coupling device to couple a rectangular and a coaxial waveguide to one another which is rugged in construction, simple in design, and of improved efiiciency.

In accordance with this invention, a waveguide coupling device couples a rectangular Waveguide adapted to propagate the dominant TE -mode to a coaxial waveguide adapted to propogate the principal TEM-mode. The waveguide coupling device has the function to reorient the electric field of the existing mode in progressive incremental stages until the electric field of the desired mode is obtained. To transform the TE -mo'de to the TEM-mode, the process of reorienting' the electric field involves the division of the dominant TE -mode into two portions of equal amplitude having their respective electric field vector E colinear and in phase. Thereupon,

the two portions are physically rotated through 180 degrees relative to each other so that the electric field vectors E are again colinear but 180 degrees out of phase. Finally the two rotated portions are recombined in such a fashion that the electric field vectors which were colinear upon the first stage of recombination are gradually reoriented until in the final stage of recombination they assume the familiar radially symmetric pattern of the TEM-mode of the coaxial waveguide.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

Fig. l is a perspective view of an embodiment of the waveguide coupling device provided in accordance with this invention;

Fig. 2 is a fragmentary perspective view of the output section of the waveguide coupling device of Fig. 1; and

Figs. 3 to 8 are cross-sectional perspective views of different portions of the wave coupling device of Fig. 1 showing the progressive reorientation of the electric field vector E.

Referring now to the drawing and particularly to Fig. 1, there is shown awaveguide coupling device 10 in accordance with this invention. For the purpose of this specification to facilitate the description of the waveguide coupling device, the device is considered as being made up of an input section 12, a center section 14 and an output section 16. Such a division is arbitrary and does not designate physical entities which are coupled to one another.

The input section 12 is essentially a Y-type power divider which is a standard rectangular waveguide 18 provided with a thin conducting plate 20 across the waveguide to form two branch waveguides 22, 24 of equal size. The branch waveguides 22, 24 are modified by tapering each branch in a waveguide of standard size 26, 28. This provides an impedance in the branch waveguides 26 28 equal to that of the main waveguide 18. The thin conducting plate 20 is increased in thickness and finally split into two plates which respectively become the bottom and top wall of the branch waveguides 26 and 28.

The center section 14 of the waveguide coupling device 10 is the continuation of the branch waveguides 26 and 28 which shows each of the two branch waveguides rotationally twisted in an opposite rotational sense about its respective axis through degrees. After the rotational twist, the branch waveguides 26 and 28 are again facing each other back to back. The two branch waveguides 26 and 28 are then joined to one another by a Y-type power added so that the broad walls 30 and 32 eventually become a thin conductive plate 34 shown in Fig. 2 and the remaining walls of the branch waveguides 26 and 28 merge into a square waveguide.

The output section 16 of the waveguide coupling dvice It) is essentially a waveguide transition from the square waveguide 36 separated into two rectangular branch waveguides 26 and 28 separated by the thin conducting plate 3-; to a coaxial waveguide 38 having an outer conductor 40 and a center conductor 42.

Fig. 2 shows with greater particularity the waveguide transition of the output section 16. The square waveguide 36 is gradually changed into the cylindrical outer conductor 40 of the coaxial waveguide 33. The thin conducting plate 34 is disconnected from the square waveguide 36 at point 44 and gradually tapered towards its center line until it forms the inner conductor 42 of the coaxial waveguide 38;

Figs. 3 to 8 are cross-sectional perspective views taken along the various lines from 3-3 to 88 along the waveguide coupling device of Fig. 1 and have been included to aid in the explanation of operation of the coupling device of this invention.

Wave energy in the TE -mode enters the input section 12 of the wave coupling device through the main waveguide 18. Fig. 3 is a section of the rectangular waveguide 18 taken along line 33 and shows the vertical orientation of the electric vector E. The Y-type power divider which feeds the branch waveguides 26 and 28 splits up the wave energy from the main waveguide 18 into two portions. Fig. 4 is a section of the branch waveguides 26 and 28 taken along line 4-4 and shows the wave energy split into two portions having their respective electric vectors parallel and colinear. As wave energy is propagated through the center section 14 of the coupling device 10, the direction of the electric vector of wave energy in waveguide 26 is rotated counterclockwise through 90 degrees and the direction of the electric vector of wave energy in waveguide 28 is rotated clockwise through 90 degrees. Fig. 5 and Fig. 6 are sections of the branch-waveguides 26 and 28 taken respectively along lines 5-5 and 66 respectively and the direction of the electric vector in each waveguide at an intermediate and at the final position of the wave energy within the center section 14. As is seen from Fig. 6, the respective electric vectors are again colinear but 180 degrees out of phase. During passage through the output section 16 of the coupling device 10, the wave energy from the branch waveguides 26 and 28 is recombined. The electric field distributions within the waveguides 26 and 28 which are represented by the electric vectors will therefore be understood to be mirror images of each other. They may be said to have a common vector center. Fig. 7 is a crosssectional view of the waveguide transition 16 illustrating the effect of the tapered thin conductive plate 34 upon the wave energy; When the plate 34 separates the square waveguide 36 into two compartments, the electric vector assumes the position shown in Fig. 6. As the plate 34 recedes from the walls 45 and 46, the electric field vector starts its reorientation towards a radial field configuration. Fig. 8 is a cross-sectional view of the coaxial waveguide 38 taken along line 8-8 and shows the TEM-mode which is the end product of the coupling device 10.

The wave coupling device provided in accordance with the present invention, therefore, provides a unity coupling between a rectangular waveguide and a coaxial waveguide. Of particular significance is that a transition from the dominant TE -mode of the rectangular waveguide to the principal TEM-mode of the coaxial waveguide has been eflfected without the use of an intermediate excitation element. Therefore the wave coupling device heretofore described is able to handle much greater amounts of power and is considerably less sensitive to changes in frequency than has heretofore been possible.

What is claimed is:

1. A waveguide coupling device to effect a unity transition between the dominant TE -mode of a rectangular waveguide and the principal TEM-mode of a coaxial waveguide comprising in combination; dividing means for equally dividing wave energy in the dominant TE -mode of a rectangular waveguide into two portions, rotating waveguide and adapted to equally divide said dominant TE -mode into two portions, rotating means responsive to said two portions of wave energy and adapted to separately and oppositely rotate each of said two portions of wave energy through an angle of 90 degrees into outof-phase electric vector colinearity, said two portions of wave energy having a common vector center, and combining means responsive to said rotated portion of wave energy and adapted to combine said two rotated portions of wave energy to provide the principal TEM-mode of a coaxial waveguide.

3. A waveguide coupling device to effect a unity transition between the dominant TE -mode of a rectangular waveguide and the principal TEM-mode of a coaxial waveguide and comprising; a rectangular Y-type power divider having two rectangular output ports, two mirror image rectangular waveguide sections each twisted in opposite rotational sense through an angle of 90 degrees and each coupled to a different one of said output ports whereby said mirror image rectangular waveguide sections provide wave energy in the dominant TE -mode having their respective field vectors colinear and 180 degrees out of phase with one another, said two portions of wave energy having a common vector center, and combining means responsive to the wave energy in each of said sections coupled to said waveguide sections, said combining means adapted to combine said two wave energy inputs to form the principal TEM-mode of said coaxial waveguide.

4. A waveguide coupling device comprising; a rectangular waveguide Y-guide power divider having two output ports, two mirror image rectangular waveguide sections having contiguous broad-wall end portions, each of said mirror image waveguide sections twisted axially and in opposite angular direction through an angle of 90 degrees and each coupled to a ditierent output port of said power divider, and a square-to-coaxial waveguide transition, said transition including an outer member having a substantially square input section and a substantially circular outmeans coupled to said dividing means for separately and waveguide and comprising; dividing means responsive to wave energy in the dominant TE -mode of a rectangular put section and whose cross-sectional shape changes progressively from square to circular, said transition also including a thin conductive wall across its input section dividing said input section into two equal rectangular waveguide portions, said two mirror image waveguide sections coupled to said two rectangular waveguide portions, said conductive wall separating from said outer member and progressively tapering towards its center line to become the center conductor of a coaxial waveguide which forms the output section of said transition.

5. A waveguide coupling device comprising: a rectangular Y-type power divider having two output waveguides, said output waveguides each being twisted axially and in opposite rotational directions through a quarter turn and thereafter recombined to form a parallel section having a common broad wall, said parallel section having said common broad wall separating from the waveguide walls and tapering down to form the center conductor of a coaxial waveguide, the remaining walls of said output waveguides comprising said parallel section also combining to form a square waveguide whose cross section progressively changes to a cylindrical waveguide constituting the outer conductor of said coaxial waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,285 Clapp Apr. 6, 1948 2,656,513 King Oct. 20, 1953 FOREIGN PATENTS 623,770 Great Britain May 23, 1949 UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECTION Patent No, 2,878,453 March 17, 1959 Robert S. Elliott Column 2, line 50, for "added" read adder 60111111114, line 31, for "Y -guide" read Y-=type Signed and sealed this 14th day of July 1959a (SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Ofl'icer Commissioner of Patents 

